The free calls app Viber is to challenge Skype's domination of the free internet phone services market by extending its service to desktop computers for the first time.

The move comes as the company announced it now has 200 million regular users, up from 140 million at the end of 2012. The figure is a major milestone for the Cyprus-based firm – but it is still dwarfed by Skype, which has more than 600 million users, and the heft of its owner, Microsoft, behind it.

Like Skype and free texting phone app Whatsapp, the Viber mobile client offers free messaging and calls. The desktop version is the first in its suite to offer video calls.

"People spend a substantial amount of time on their smartphones. However, a lot of that usage takes place at home or in the office, where they have laptops or desktops close by," said the Viber chief executive, Talmon Marco.

The release of Viber Desktop is part of the rollout of Viber 3.0, a release which will include major updates to both the Android and iOS versions, as well as a new version for BlackBerry.

The company has also added eight new languages as part of its bid to take on Skype, which transformed international communication when it launched its free phone service 10 years ago. Though not compatible with existing voice-over-internet-protocol (VoIP) systems using the SIP protocol, Skype grew more rapidly because its peer-to-peer system ensured better call quality and lower latency than other VoIP setups.

Since then, Skype has launched video calls, recently adding HD-quality video, and last week its owner Microsoft – which paid $8.5bn (£5.5bn) for the company in 2011 – announced it was integrating the Skype service with Outlook webmail services.